Wireless LAN with channel swapping between DFS access points

ABSTRACT

The present invention enhances the dynamic frequency selection 9DFS) algorithms used in Wireless LANs by adding a channel swapping mechanism. The aim of the traditional DFS algorithm is to dynamically select channels in a wireless LAN in such a way that the best performance is achieved. However, not always the optimal channel selection is achieved. This invention describes an addition to the DFS algorithm in such a way that two APs can decide to swap channels instead of one AP switching to another channel. To avoid the problem of sub-optimal channel selection, a requesting AP sends Swap Requests to other APs in order to sense the willingness of other APs to swap channels with the requesting AP.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/141,189, filed on May 8, 2002 and issued as U.S. Pat. No. 7,499,964,which itself claims priority of European Patent Application No.01304146.2, which was filed on May 8, 2001, the contents of both ofwhich are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to a communication system comprising aplurality of access points (APs) and network stations, each said networkstation being arranged to communicate with one of said access pointsthrough a wireless communication protocol. The invention also relates toaccess points for such a communication system.

BACKGROUND OF THE INVENTION

Wireless local area networks (LANs) have been developed as an enhancedreplacement for wired LANs. In a wireless LAN for data-communication aplurality of (mobile) network stations (e.g., personal computers,telecommunication devices, etc.) are present that are capable ofwireless communication. As compared to wired LANs, data-communication ina wireless LAN can be more versatile, due to the flexibility of thearrangement of network stations in the area covered by the LAN, and dueto the absence of cabling connections.

Wireless LANs are generally implemented according to the standard asdefined by the ISO/IEC 8802-11 international standard (IEEE 802.11).IEEE 802.11 describes a standard for wireless LAN systems that willoperate in the 2.4-2.5 GHz ISM (industrial, scientific and medical)band. This ISM band is available worldwide and allows unlicensedoperation for spread spectrum systems. For both the US and Europe, the2,400-2,483.5 MHz band has allocated, while for some other countries,such as Japan, another part of the 2.4-2.5 GHz ISM ban has beenassigned. The IEEE 802.11 standard focuses on the MAC (medium accesscontrol) and PHY (physical layer) protocols for AP based networks andadhoc networks.

In AP based wireless networks, the stations within a group or cell cancommunicate only directly to the AP. This AP forwards messages to thedestination station within the same cell or through the wireddistribution system to another AP, from which such messages arrivefinally at the destination station. In ad-hoc networks, the stationsoperate on a peer-to-peer level and there is no AP or (wired)distribution system.

The 802.11 standard supports three PHY protocols: DSSS (direct sequencespread spectrum), FHSS (frequency hopping spread spectrum), and infraredwith PPM (pulse position modulation). All these three PHYS provide bitrates of 1 and 2 Mbit/s. Furthermore, IEEE 802.11 includes extensions 11a and 11 b which allow for additional higher bit rates: Extension 11 bprovides bit rates 5.5 and 11 Mbit's as well as the basic DSSS bit ratesof 1 and 2 Mbit/s within the same 2.4-2.5 GHz ISM band. Extension 11 aprovides a high bit rate OFDM (orthogonal Frequency DivisionMultiplexing modulation) PHY standard providing bit rates in the rangeof 6 to 54 Mbit/s in the 5 GHz band.

The IEEE 802.11 basic MAC protocol allows interoperability betweencompatible PHYs through the use of the CSMA/CA (carrier sense multipleaccess with collision avoidance) protocol and a random back-off timefollowing a busy medium condition. The IEEE 802.11 CSMA/CA protocol isdesigned to reduce the collision probability between multiple stationsaccessing the medium at the same time. Therefore, a random back-offarrangement is used to resolve medium contention conflicts. In addition,the IEEE 802.11 MAC protocol defines special functional behaviour forfragmentation of packets, medium reservation via RTS/CTS(request-to-send/clear-to-send) polling interaction and pointcoordination (for time-bounded services).

Moreover, the IEEE 802.11 MAC protocol defines Beacon frames sent atregular intervals by the AP to allow stations to monitor the presence ofthe AP. The IEEE 802.11 MAC protocol also gives a set of managementframes including Probe Request frames which are sent by a station andare followed by the Probe Response frames sent by an available AP. Thisprotocol allows a station to actively scan for APs operating on otherfrequency channels and for the APs to show to the stations whatparameter settings the APs are using.

Every DSSS AP operates on one channel. The number of channels depends onthe regulatory domain in which the wireless LAN is used (e.g. 11channels in the U.S. in the 2.4 GHz band). The number can be found inISO/IEC 8802-011, ANSI/IEEE Std 802.11 Edition 1999-00-00. Overlappingcells using different channels can operate simultaneously withoutinterference if the channel distance is at least 3. Non-overlappingcells can always use the same channels simultaneously withoutinterference. Channel assignment can be dynamic or fixed. Dynamicchannel assignment is preferable, as the environment itself is dynamicas well.

SUMMARY OF THE INVENTION

The present invention relates to an access point for a wireless LANcommunication network, arranged to:

monitor its access point traffic load

send probe requests and probe responses to other access points

receive probe requests and probe responses from other access points

include information on the traffic load in the probe responses

calculate and store an interference parameter for each of a plurality ofits possible channels

calculate and store a channel sharing parameter for each of theplurality of channels

calculate a regular channel quality parameter for each of the pluralityof channels, indicative of the amount of interference and channelsharing on each of the plurality of channels, using the interference andchannel sharing parameters

dynamically select an optimum channel from the plurality of possiblechannels using the regular channel quality parameters,

wherein the access point is arranged to select the optimum channel bymutually swapping channels with another access point using a swappingmechanism.

By introducing a swapping option between adjacent access points, thepresent invention provides a better overall performance for the wirelessLAN.

Moreover, the present invention relates to a wireless LAN communicationnetwork, comprising at least two access points as described above.

Furthermore, the present invention relates to a method of selecting anoptimum channel by an access point in a wireless LAN communicationnetwork, comprising the steps of:

monitor its access point traffic load

send probe requests and probe responses to other access points

receive probe requests and probe responses from other access points

include information on the traffic load in the probe responses

calculate and store an interference parameter for each of a plurality ofits possible channels

calculate and store a channel sharing parameter for each of theplurality of channels

calculate a regular channel quality parameter for each of the pluralityof channels, indicative of the amount of interference and channelsharing on each of the plurality of channels, using the interference andchannel sharing parameters

dynamically select an optimum channel from the plurality of possiblechannels using the regular channel quality parameters,

wherein the access point is arranged to select the optimum channel bymutually swapping channels with another access point using a swappingmechanism.

The present invention also relates to a computer program product to beloaded by an access point for a wireless LAN communication network, thecomputer program product providing the access point with the capacityto:

monitor its access point traffic load

send probe requests and probe responses to other access points

receive probe requests and probe responses from other access points

include information on the traffic load in the probe responses

calculate and store an interference parameter for each of a plurality ofits possible channels

calculate and store a channel sharing parameter for each of theplurality of channels

calculate a regular channel quality parameter for each of the pluralityof channels, indicative of the amount of interference and channelsharing on each of the plurality of channels, using the interference andchannel sharing parameters

dynamically select an optimum channel from the plurality of possiblechannels using the regular channel quality parameters,

wherein the access point is arranged to select the optimum channel bymutually swapping channels with another access point using a swappingmechanism.

Moreover, the present invention relates to a data carrier provided witha computer program product as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Below, the invention will be explained with reference to some drawings,which are, intended for illustration purposes only and not to limit thescope of protection as defined in the accompanying claims.

FIG. 1 a shows the cells of three APs in a wireless LAN in the PriorArt.

FIG. 1 b shows the cells of four APs in a wireless LAN in the Prior Art.

FIG. 1 c shows the cells of four APs in a wireless LAN as described inthe invention.

FIG. 2 shows a block diagram of the arrangement of the present inventionfor a wireless LAN interface card.

FIG. 3 shows a schematic block diagram of a network station in thepresent invention.

FIG. 4 shows a schematic block diagram of an access point (AP) in thepresent invention.

FIG. 5 shows a flow diagram of the swapping procedure of a requesting APin the present invention.

FIG. 6 shows a flow diagram of the swapping procedure of a responding APin the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the co-owned, co-pending, U.S. patent application Ser. No.10/140,689, filed 8 May 2002, entitled “Network System Comprising AccessPoint” (our reference Awater 12-23-14), the contents of which areincorporated by reference herein, dynamic assignment of channels iscalled dynamic frequency selection (DFS). The aim of the DFS algorithmis to dynamically assign channels in a wireless LAN in such a way thatthe best performance is achieved. Performance can be expressed in termsof throughput, delay and fairness. An AP with dynamic frequencyselection is able to switch its channel in order to obtain a betteroperating channel. It will usually choose a channel with lessinterference and channel sharing than that on the current channel.

In the algorithm of the Awater 12-23-14 application, the amount ofinterference an AP is experiencing on a certain channel X, is expressedby a parameter I(X). Channel sharing is expressed by a parameter CS(X).The values of CS(X) are combined to calculate a so-called ChannelSharing and Interference Quality CSIQ(X). The value of CSIQ(X) is ameasure for the amount of interference and channel sharing belonging toa certain channel X. In one embodiment:

CS(X) = Share  (RX_L(X)) * Load(X) and${I(X)} = {{{Noise\_ L}(j)} + \underset{\_}{{\sum\limits_{j = 1}^{X - 1}{Y(j)}} + {\sum\limits_{j = {X + 1}}^{N}{Y(j)}}}}$where:Y(j)=(RX _(—) L(j)−RJ(j−X))*Load(j),

-   -   RX_L(X) corresponds to a reception level of a response signal        with channel frequency X,    -   Share (RX_L(X)) equals 0 if RX_L(X) is below 10 dB under the        signal detection threshold,    -   Share (RX_L(X)) equals 0.1 if RX_L(X) is above 10 dB and under 9        dB below the signal detection threshold,    -   Share (RX_L(X)) equals i/10 if RX_L(X) is above 10−i+1 dB and        under 10-i dB below the signal detection threshold, for i=2, . .        . , 8,    -   Share (RX_L(X)) equals 0.9 if RX_L(X) is above 2 dB and under 1        dB below the signal detection threshold,    -   Share (RX_L(X)) equals 1 if RX_L(X) is above 1 dB below the        signal detection threshold,    -   Load(X) corresponds to the load on channel frequency X,    -   Noise_L(j) corresponds to the noise level of channel frequency        j,    -   N is the total number of channel frequencies,    -   RX_L(j) corresponds to a reception level of a response signal        with channel frequency j,    -   RJ(j−X) corresponds to a rejection level of a signal with        channel frequency j on channel frequency X, and    -   Load(j) corresponds to the load on channel frequency j.

In the Awater 12-23-14 application, an AP will switch to a channel Y ifthe value of CSIQ(Y) is the highest of all the values CSIQ(X) of thechannels X=1, . . . N with the number of available channels. So the bestchannel quality is represented by the highest CSIQ(X). The functioningof the DFS algorithm in the Awater 12-23-14 application, will beexplained in an example with help of FIGS. 1 a and 1 b. The wireless LAN1, shown in FIG. 1 a, comprises a number of access points of which threeaccess points AP1, AP2, AP3 are shown. These access points serve asaccess point for their respective cells 3,5,7 which are eachschematically depicted by a circle around their respective access point.In the initial situation, the access points AP1, AP2, AP3 arecommunicating with their network stations on channels C1, C2, C3,respectively. The cells 3,5,7 may have different sizes. Cell size isdepending on the desired coverage area of an access point and on therequirements of data throughput in the cell. The cell size can becontrolled by suitable setting of the levels of the defer behaviourthreshold and carrier sense detection threshold as known fromEP-A-0903891. For example, a cell may comprise a number of networkstations, NS1, NS2 that require high throughputs. In that case, the cellsize should be small such that other network stations will be left outof the cell as much as possible. In another case, for example, in a cellonly few network stations with low throughput requirements will bepresent. Then, a single large cell comprising these network stationswill be sufficient to handle all data traffic related to that cell. FIG.1 a shows the initial situation of a wireless LAN 1 comprising threeDFS-capable Aps. In the LAN 1 a plurality of network stations NS1, NS2is present of which only two are shown. In FIG. 1 a, for example, thenetwork station NS1 is communicating with the access point AP1 for allits data traffic. The network station NS1 itself continuously monitorsthe communication quality (i.e. the difference between signal receptionlevel and average noise level) of its communication with the accesspoint AP1. As long as a good communication quality for the associatedaccess point AP1 is maintained, the network station NS1 stayscommunicating with AP1. When the communication quality decreases below apredetermined level, the network station NS1 starts to search foranother cell 5 (an access point AP2) with a better communicationquality. To this purpose, the network station NS1 is probing theassociated access point AP1 and all other access points (i.e. AP2)within range, as known to persons skilled in the art. In this procedurethe network station NS1 uses the signal reception level of Beacon framesreceived from the associated access point AP1 and Probe Response framesfrom the other access point AP2. The Probe Response frames are receivedby the network station NS1 following Probe Request frames sent by thenetwork station NS1. As known from IEEE 802.11, the other access pointAP2 will be operating on a channel with another frequency than the oneof access point AP1. Network station NS2, shown in FIG. 1 a, iscommunicating with AP2. When the communication quality decreases, thisnetwork station NS2 also will start to search for another cell with abetter communication quality but will not be able to find a better AP sonetwork station NS2 will stay communicating with AP2.

FIG. 1 b shows the situation where a non-DFS access point AP4 using, forexample channel 9, has arrived within the range of the DFS-capable AP1.With the DFS algorithm of the Awater 12-23-14 application, access pointAP1, operating on channel 10, will switch to channel 4 or to channel 11in order to have at least a channel distance of 2 with every neighboringcell.

A problem of the DFS algorithm described in the Awater 12-23-14application is the inability to optimize the overall performance. AllAps in a wireless LAN will currently optimize their own performance andwill not take performance of other APs into consideration. It may wellbe that, from a network point of view, the division of the channels overthe difference APs is not optimal.

In FIG. 1 c a schematic overview of a preferred embodiment is shown. Awireless LAN1 comprises a set of access points AP1, AP2, AP3 which haveoverlapping cells 3,5,7. In this way (mobile) network stations are ableto communicate with an AP in a continuous area. Besides LAN1 a fourthaccess point AP4 is present having an accompanying cell 9. As in thesituation described with reference to FIG. 1 b, it is assumed that AP4is a non-DFS AP. However, it should be understood that AP4 may be anykind of radio source acting on channel C4. The circles 43 and 45 depictthe positions in which the receive level equals the lowest possiblecarrier detect threshold of respectively AP1 and AP2.

FIG. 2 shows an example of a block diagram of an arrangement of thepresent invention for a medium access controller (MAC) device 11 on awireless LAN interface card 30 installed in network station NS1, NS2 oron a similar wireless LAN interface card 130 installed in access pointAP1, AP2, respectively.

Here, the MAC device 11 is schematically depicted, showing only asignal-processing unit 12, a signal reception level detection circuit13, an antenna 31 and an on-board memory 14 as needed for thedescription of this embodiment of the invention. The MAC device 11 maycomprise other components not shown here. Also, the components 12,13,14which are shown, may be separate devices or integrated into one device.As desired, the devices also may be implemented in the form of analog ordigital circuits. The on-board memory 14 may comprise RAM, ROM, FlashROMand/or other types of memory devices, as are known in the art.

FIG. 3 shows a schematic block diagram of an embodiment of a networkstation NS1, NS2 comprising processor means 21 with peripherals. Theprocessor means 21 is connected to memory units 18,22,23,24 which storeinstructions and data, one or more reading units 25 (to read, e.g.,floppy disks 19, CD ROM's 20, DVD's, etc.), a keyboard 26 and a mouse 27as input devices, and as output devices, a monitor 28 and a printer 29.Other input devices, like a trackball and a touch screen, and outputdevices may be provided for. For data-communication over the wirelessLAN 1, and interface card 30 is provided. The interface card 30 connectsto an antenna 31.

The memory units shown comprise RAM 22, (E)EPROM 23, ROM 24 and harddisk 18. However, it should be understood that there may be providedmore and/or other memory units known to persons skilled in the art.Moreover, one or more of them may be physically located remote from theprocessor means 21, if required. The processor means 21 are shown as onebox, however, they may comprise several processing units functioning inparallel or controlled by one main processor, that may be located remotefrom one another, as is known to persons skilled in the art.

In an alternative embodiment of the present invention, the networkstation 5,6 may be a telecommunication device in which the components ofinterface card 30 are incorporated as known to those skilled in the art.

FIG. 4 shows a schematic block diagram of an embodiment of an accesspoint AP1, AP2, AP3 comprising processor means 121 with peripherals. Theprocessor means 121 are connected to memory units 118,122,123,124 whichstore instructions and data, one or more reading units 125 (to read,e.g., floppy disks 119, CD ROM's 120, DVD's, etc.), a keyboard 126 and amouse 127 as input devices, and a output devices, a monitor 128 and aprinter 129. For data-communication over the wireless LAN 1, aninterface card 130 is provided. The interface card 130 connects to anantenna 131. Furthermore, the access point AP1, AP2, AP3 is connected toa wired distribution network 140 through I/O means 132 for communicationwith, e.g., other access points. The memory units shown comprise RAM133, (E)EPROM 123, ROM 124 and hard disk 118. However, it should beunderstood that there may be provided more and/or other memory unitsknown to persons skilled in the art. Moreover, one or more of them maybe physically located remote from the processor means 121, if required.The processor means 121 are shown as one box, however, they may compriseseveral processing units functioning in parallel or controlled by onemain processor, that may be located remote from one another, as is knownto persons skilled in the art. Moreover, other input/output devices thanthose shown (i.e. 126,127,128,129) may be provided.

In an alternative embodiment of the present invention, the access pointAP AP2, AP3 may be a telecommunication device in which the components ofinterface card 130 are incorporated as known to those skilled in theart.

The appearance of a new access point AP4 shown in FIG. 1 c will causesudden interference to AP1 because it is using channel C4=9 which has achannel distance less than 3 to the channel C1=10 of AP1. Now, inaccordance with the invention, access point AP1 decides to start aswapping procedure.

FIG. 5 shows a flow diagram of the swapping procedure for the requestingaccess point AP1. In the procedure of FIG. 5 the following parametersare used:

-   regCSIQ this is a quality parameter calculated for every possible    channel on which the AP can operate; its value is a measure for both    channel sharing and interference for the channel concerned. The    formula is given by:    regCSIQ(X)=CS(X)+CorFac×I(X)    -   In contrast with the CSIQ in the Awater 12-23-14 application,        the lower the value for regCSIQ(X), the better the channel X.        The formulas for CS (X) and 1(X) are found in the Awater        12-23-14 application; the parameter CorFac is a correction        factor that is preferably equal to 1.-   ssCSIQ swap specific CSIQ; this is a specially calculated quality    parameter. The formula is given by:    ssCSIQ(X)=regCSIQ′(X)+SwapPenalty    -   where regCSIQ′(X) is calculated in the same was as regCSIQ(X)        but under the assumption that a responding AP already uses the        channel of a requesting AP, i.e., a situation is assumed in        which swapping has already occurred. The SwapPenalty is a        parameter indicating that swapping is associated with a certain        penalty. It may be zero but preferably it has a positive value,        e.g. 10.

At the start of the swapping procedure, access point AP1 is usingchannel C1=10. At step 51 the requesting access point AP1 collectsinterference and sharing information by means of sending Probe Requeststo other APs. Then at step 52, AP1 calculates the regCSIQ values for allpossible channels. At step 53, AP1 calculates a swap specific CSIQ(ssCSIQ) for every channel used by any AP responding to the ProbeRequest. For the calculation of the swap specific CSIQ values, theformula for regCSIQ is used, but with the assumption that the respondingaccess points AP2, AP3 are not using the channel on which they areactually operating, but the channel on which the requesting AP isoperating.

The swap specific CSIQ value is increased by a certain amount, (e.g., by10). A swap should not be executed when it is not necessary, because ofpossible overhead costs. By increasing the ssCSIQ by e.g. 10, it becomesmore likely that a channel with a regular CSIQ is selected for switchingand swapping is not necessary.

Now at step 55, the lowest CSIQ is determined out of all the calculatedregCSIQ values and all the ssCSIQ values. If the lowest ssCSIQ issmaller than the lowest regCSIQ the procedure will go on to step 57. Ifthis in not the case step 69 will be executed. At step 57, AP1calculates the difference between the lowest regCSIQ and the lowestssCSIQ. This difference, named SwapBinP_(AP1), is the benefit inperformance for AP1 if AP1 would swap channels (with the APcorresponding to the lowest ssCSIQ) instead of switching its channel tothe channel corresponding to the lowest regCSIQ. At step 59, a SwapRequest is sent using the channel corresponding to the lowest ssCSIQvalue. The swap request contains the channel C1 of AP1 requesting theswap, and it also contains the value for SwapBinP_(AP1).

Now at step 61, the access point AP1 will wait for a Swap Responseduring a predefined time period T_wait. If AP1 has received a SwapResponse within T_wait ms, the result of step 63 is YES and step 65follows. If the result of the test at step 63 is NO, then the next stepwill be step 69 and the channel will be switched to a channel Cs,corresponding to the lowest regCSIQ.

At step 65, the Swap Response is checked. If the Swap Response is ‘yes’,then step 67 follows. This means that AP1 will change its channel to thevalue of the one of the responding access point AP2 (i.e., C2). If atstep 65 the Swap Response is ‘no’, step 69 will be executed and AP1 willswitch to said channel C5.

FIG. 6 shows a flow diagram of the swapping procedure for the respondingaccess point AP2. At the start of the procedure, access point AP2 isusing channel C2=6. At step 75, access point AP2 is operating normallyand is stand-by for any Swap Request. If, at step 77, a request isreceived, AP2 will proceed to step 79. If no Swap Request is receivedAP2 will stay at step 75. At step 79, the access point AP2 will rescanall the channels in order to get the Probe Responses of neighbouringAPs. During the scan of a channel X, AP2 switches to the channel inquestion (i.e. X) and configures itself temporarily to the lowest deferthreshold and bit rate to allow communication over as large as possibledistance, see circle 45 in FIG. 1 c. AP2 sends a Probe Request frame toevoke a probe Response from all APs tuned to the channel in question andwithin radio range. The Probe Response packets sent by the APsresponding to the Probe Request, carry information on load factors fromeach AP using the channel in question. The gathered load informationfrom all the probe-responding APs together with the receive levels ofthe Probe Responses, are stored by AP2. This is done for all thechannels and in the same way as in the Awater 12-23-14 application.

Next, at step 80, the regCSIQ value for the operating channel of AP2 iscalculated. This means regCSIQ(C2) is calculated. At step 81, the valueof ssCSIQ is calculated for the channel that is used by the swaprequesting AP1. This means ssCSIQ(C1) is calculated using the load andreceive level information stored by AP2 at step 79. Then at step 83,access point AP2 switches its channel to the one of the swap requestingAP1 (i.e., C1). At step 85, the value of ssCSIQ(C1) is compared to thevalue of regCSIQ(C2). If ssCSIQ(C1) is lower than regCSIQ(C2), thenaccess point AP2 will send a Swap Response ‘yes’ at step 87. IfssCSIQ(C1) is not lower than regCSIQ(C2) the procedure will go to step88. In step 88 the administrative domain (e.g. company or organization)of AP1 is compared with the one of AP2. If the domains are not the same,step 90 is executed. If the two domains match, then step 89 will followin which another, so-called ‘sacrifice’ test is done. At this step thebenefit in performance for, and predicted by, requesting AP1 (i.e.,SwapBinP_(AP1), e.g., the difference between the lowest of all regularchannel quality parameters (regCSIQ) and the lowest of all swap specificchannel quality parameters (ssCSIQ)) is compared to the predicteddecrease in performance for AP2 (i.e., ssCSIQ(C1)−regCSIQ(c2)). If thebenefit in performance for AP1 is higher than the decrease inperformance for AP2, access point AP2 will sacrifice its channel andwill agree to swap channels. This means that step 87 will follow. If theanswer to the test in step 88 is NO, then step 90 follows. This meansthat AP2 will send a Swap Response ‘no’ to the swap requesting AP1.After this, AP2 will switch its channel back to CS=6, see step 91.

The swapping procedure described above is not a low-overhead solution.Therefore, it should not be attempted frequently. It should only beattempted once per channel change. Once a swap has failed for a certainAP, it should not be attempted in the near future. Therefore, theinformation record that exists for every DFS-capable AP, also contains atimer. This timer is used to ensure that swap requests to the same APare separated by a certain number of hours (i.e., 24).

1. A first access point for a wireless LAN communication network,wherein the first access point is adapted to: (a) send probe requestsand probe responses to other access points, (b) receive probe requestsand probe responses from other access points, (c) calculate aninterference parameter for each of a plurality of its possible channels,(d) calculate a channel sharing parameter for each of the plurality ofchannels, (e) calculate a regular channel quality parameter (regCSIQ)for each of the plurality of channels, indicative of the amount ofinterference and channel sharing on each of the plurality of channels,using the interference and channel sharing parameters, and (f)dynamically select a new channel from the plurality of possible channelsusing the regular channel quality parameters (regCSIQ), wherein: thefirst access point is arranged to select the new channel by mutuallyswapping channels with a second access point using a swapping mechanismin which: the new channel for the first access point is the previouschannel for the second access point; and the new channel for the secondaccess point is the previous channel for the first access point; and thefirst access point is further adapted to monitor traffic load, whereinthe probe responses include traffic load information (i) carried in theprobe responses and (ii) corresponding to the traffic load at the accesspoints that send the probe responses.
 2. The first access pointaccording to claim 1, wherein the first access point is a swaprequesting access point (AP1), operating on a first channel (C1), thatcalculates and stores a swap specific channel quality parameter (ssCSIQ)for every responding access point (AP2) operating on a second channel(C2), the swap specific channel quality parameter (ssCSIQ) beingcalculated under the assumption that every responding access point (AP2)and the swap requesting access point (AP1) have already swappedchannels, which swap specific channel quality parameter is used in theswapping mechanism.
 3. The first access point according to claim 1,wherein the first access point is arranged to use the swapping mechanismonly after a predetermined time has lapsed since a last time of usingthe swapping mechanism.
 4. The first access point according to claim 1,wherein: the wireless LAN communication network uses a carrier sensemultiple access with collision avoidance (CSMA/CA) protocol; and thefirst access point is adapted to communicate with multiple networkstations using a single channel under the CSMA/CA protocol.
 5. Awireless LAN communication network comprising at least two access pointsaccording to claim
 1. 6. The wireless LAN communication networkaccording to claim 5, wherein: the wireless LAN communication networkuses a carrier sense multiple access with collision avoidance (CSMA/CA)protocol; and the first access point is adapted to communicate withmultiple network stations using a single channel under the CSMA/CAprotocol.
 7. Method of selecting a new channel by a first access pointin a wireless LAN communication network, comprising the steps of: (a)sending probe requests and probe responses to other access points; (b)receiving probe requests and probe responses from other access points;(c) calculating an interference parameter for each of a plurality of itspossible channels; (d) calculating a channel sharing parameter for eachof the plurality of channels; (e) calculating a regular channel qualityparameter (regCSIQ) for each of the plurality of channels, indicative ofthe amount of interference and channel sharing on each of the pluralityof channels, using the interference and channel sharing parameters; and(f) dynamically selecting the new channel from the plurality of possiblechannels using the regular channel quality parameters (regCSIQ),wherein: the first access point is arranged to select the new channel bymutually swapping channels with a second access point using a swappingmechanism in which: the new channel for the first access point is theprevious channel for the second access point; and the new channel forthe second access point is the previous channel for the first accesspoint; and the first access point monitors traffic load, wherein theprobe responses include traffic load information (i) carried in theprobe responses and (ii) corresponding to the traffic load at the accesspoints that send the probe responses.
 8. A method according to claim 7,wherein the first access point is a swap requesting access point (AP1),operating on a first channel (C1), that calculates and stores a swapspecific channel quality parameter (ssCSIQ) for every responding accesspoint (AP2) operating on a second channel (C2), the swap specificchannel quality parameter (ssCSIQ) being calculated under the assumptionthat every responding access point (AP2) and the swap requesting accesspoint (AP1) have already swapped channels, which swap specific channelquality parameter is used in the swapping mechanism.
 9. The methodaccording to claim 7, wherein: the wireless LAN communication networkuses a carrier sense multiple access with collision avoidance (CSMA/CA)protocol; and the first access point is adapted to communicate withmultiple network stations using a single channel under the CSMA/CAprotocol.
 10. The first access point according to claim 1, wherein,following failure of a first swap request received from an other accesspoint to swap channels with the other access point, the first accesspoint sets a timer that prevents processing of another swap request forthe predetermined time.
 11. The first access point according to claim 1,wherein the channel sharing parameter is calculated as a function of thetraffic load for the corresponding channel.
 12. The method according toclaim 7, wherein the channel sharing parameter is calculated as afunction of the traffic load for the corresponding channel.